Verified successfully on focal-proposed:

root@f1:~# apt policy software-properties-common
software-properties-common:
  Installed: 0.98.9.5
  Candidate: 0.98.9.5
  Version table:
 *** 0.98.9.5 500
        500 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     0.98.9.4 500
        500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
     0.98.9.2 500
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
     0.98.9 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

root@f1:~# sudo add-apt-repository cloud-archive:xena --yes
Reading package lists...
Building dependency tree...
Reading state information...
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'sudo apt autoremove' to remove it.
The following NEW packages will be installed:
  ubuntu-cloud-keyring
0 upgraded, 1 newly installed, 0 to remove and 21 not upgraded.
Need to get 5688 B of archives.
After this operation, 22.5 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 ubuntu-cloud-keyring all 2020.02.11.4 [5688 B]
Fetched 5688 B in 0s (25.8 kB/s)
Selecting previously unselected package ubuntu-cloud-keyring.
(Reading database ... 31590 files and directories currently installed.)
Preparing to unpack .../ubuntu-cloud-keyring_2020.02.11.4_all.deb ...
Unpacking ubuntu-cloud-keyring (2020.02.11.4) ...
Setting up ubuntu-cloud-keyring (2020.02.11.4) ...
Hit:1 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease                                                                  
Get:3 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-updates/xena InRelease [7616 B]                            
Get:4 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-updates/xena/main amd64 Packages [155 kB]
Hit:5 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:6 http://archive.ubuntu.com/ubuntu focal-proposed InRelease
Hit:7 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Fetched 162 kB in 1s (125 kB/s)
Reading package lists... Done

root@f1:~# sudo add-apt-repository cloud-archive:xena-proposed --yes
Reading package lists...
Building dependency tree...
Reading state information...
ubuntu-cloud-keyring is already the newest version (2020.02.11.4).
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'sudo apt autoremove' to remove it.
0 upgraded, 0 newly installed, 0 to remove and 28 not upgraded.
Get:1 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-proposed/xena InRelease [7618 B]
Hit:2 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-updates/xena InRelease                                                       
Get:3 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-proposed/xena/main amd64 Packages [155 kB]  
Hit:4 http://archive.ubuntu.com/ubuntu focal InRelease                      
Get:5 http://security.ubuntu.com/ubuntu focal-security InRelease [109 kB]   
Hit:6 http://archive.ubuntu.com/ubuntu focal-updates InRelease                         
Hit:7 http://archive.ubuntu.com/ubuntu focal-proposed InRelease
Hit:8 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Fetched 272 kB in 1s (259 kB/s)                          
Reading package lists... Done

root@f1:~# apt policy python3-openstackclient
python3-openstackclient:
  Installed: (none)
  Candidate: 5.5.0-0ubuntu1~cloud0
  Version table:
     5.5.0-0ubuntu1~cloud0 500
        500 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-proposed/xena/main amd64 Packages
        500 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-updates/xena/main amd64 Packages
     5.2.0-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

root@f1:~# sudo apt install --yes python3-openstackclient
...

root@f1:~# apt policy python3-openstackclient
python3-openstackclient:
  Installed: 5.5.0-0ubuntu1~cloud0
  Candidate: 5.5.0-0ubuntu1~cloud0
  Version table:
 *** 5.5.0-0ubuntu1~cloud0 500
        500 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-proposed/xena/main amd64 Packages
        500 http://ubuntu-cloud.archive.canonical.com/ubuntu focal-updates/xena/main amd64 Packages
        100 /var/lib/dpkg/status
     5.2.0-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

root@f1:~# openstack --version
openstack 5.5.0